It is known that ceric oxide may be used as a catalyst or catalyst support. It is also well known that the effectiveness of a catalyst generally increases as the contact area between the catalyst and the reactants increases. In order to achieve this, it is necessary that the catalyst be kept in a state which is as finely divided as possible, that is to say that the solid particles which constitute it are as small and as individualized as possible. The fundamental role of the support is therefore to keep the catalyst particles or crystallites in contact with the reactant, in the most finely divided state possible.
During the prolonged use of a catalyst support, a reduction in the specific surface area occurs due to the coalescence of the porosity of the product. During this coalescence, some of the catalyst is encompassed in the bulk of the support and can no longer be in contact with the reactants.
The known ceric oxides have a specific surface area which decreases rapidly for operating temperatures above 500° C. and which may be very low at even higher temperatures, that is to say between 900° C. and 1000° C. Therefore, these oxides can no longer be used under these temperature conditions.